Rhodococcus ‘Jekyll and Hyde’ Bacteria Discovered in Plant Nurseries

Rho_fas3
Multiple shoot development (Danny Vereecke)

Researchers at Oregon State University (OSU) have used genome sequencing to identify species of the soil bacteria genus Rhodococcus that is commonly associated with stimulated growth patterns in a number of plant species. Herbaceous perennials such as chrysanthemum, speedwell and Shasta daisy are primarily affected by this bacterium.

Rhodococcus species are known to alter their impacts on affected plants between beneficial and pathogenic, by causing accelerated growth or deformation of plant tissues. The cause of this ability for the bacteria to change between ‘positive’ and “negative” is due to a virulence plasmid DNA molecule. Plasmids are separate from bacterial chromosomes and are therefore able to be transferred between bacteria, making it difficult to track bacteria plant diseases.

The potential for beneficial bacteria found within plant soil to alter into pathogenic bacteria has major implications on plant nurseries due to infected deformed plants being commercially less valuable, for example, Oregon’s greenhouse and nursery industry alone is worth $900 million.

The findings from this study were published on 12th December 2017 via the journal eLife. Due to the research that was undertaken within this study, plant diagnosticians now know how Rhodococcus behaves in nursery environments. With OSU developing and patenting molecular tools which will work with commercially available products to allow users to rapidly differentiate between beneficial and pathogenic Rhodococcus.

This study was initially set up due to unusual symptoms being found in pistachio trees (Pistacia vera). Individuals were shorter, wider and wouldn’t graft successfully. This was initially believed to be because of the pathogenic Rhodococcus; however, this was later identified as actually the “beneficial bacteria” via the analysis of over 100 soil samples. With the Oregon Department of Agriculture stating, “Beneficial strains of Rhodococcus causing growth changes could be mistakenly interpreted as disease symptoms.”

Further information released on this subject can be found in the original article published by EurekAlert, available here:

eurekalert.org/…2017-12/osu-opp121217.php

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Leafy gall on tobacco (Danny Vereecke)

Research into the effects of Rhodococcus infections on plant species has also been undertaken with tobacco, in which R. fascians infection was found to cause accelerated growth within BY-2 cells and result in altered gene expression, available here:

onlinelibrary.wiley.com/…2007.02062.x/pdf

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